The eye is a remarkably complex and elegant optical sensor in which light from external sources is focused, by a lens, onto the surface of the retina, an array of wavelength-dependent photosensors. As with any lens-based optical device, each of the various shapes that the eye lens can adopt is associated with a focal length at which external light rays are optimally or near-optimally focused to produce inverted images on the surface of the retina that correspond to external objects observed by the eye. The eye lens, in each of the various shapes that the eye lens can adopt, optimally or near-optimally, focuses light emitted by, or reflected from, external objects that lie within a certain range of distances from the eye, and less optimally focuses, or fails to focus, objects that lie outside that range of distances.
In normal individuals, the axial length of the eye, or distance from the lens to the surface of the retina, corresponds to a focal length for near-optimal focusing of distant objects. The eyes of normal individuals focus distant objects without nervous input to muscles which apply forces to alter the shape of the eye lens, a process referred to as “accommodation.” Closer, nearby objects are focused, by normal individuals, as a result of accommodation. Many people suffer from eye-length-related disorders, such as myopia, in which the axial length of the eye is longer than the axial length required to focus distant objects without accommodation. Myopic individuals view closer objects, within a range of distances less than typical distant objects, without accommodation, the particular range of distances depending on the axial length of their eyes, the shape of their eyes, overall dimensions of their eyes, and other factors. Myopic patients see distant objects with varying degrees of blurriness, again depending on the axial length of their eyes and other factors. While myopic patients are generally capable of accommodation, the average distance at which myopic individuals can focus objects is shorter than that for normal individuals. In addition to myopic individuals, there are hyperopic individuals who need to accommodate, or change the shape of their lenses, in order to focus distant objects.
In general, babies are hyperopic, with eye lengths shorter than needed for optimal or near-optimal focusing of distant objects without accommodation. During normal development of the eye, referred to as “emmetropization,” the axial length of the eye, relative to other dimensions of the eye, increases up to a length that provides near-optimal focusing of distant objects without accommodation. In normal individuals, biological processes maintain the near-optimal relative eye length to eye size as the eye grows to final, adult size. However, in myopic individuals, the relative axial length of the eye to overall eye size continues to increase during development, past a length that provides near-optimal focusing of distant objects, leading to increasingly pronounced myopia.
The rate of incidence of myopia is increasing at alarming rates in many regions of the world. Until recently, excessive reading during childhood was believed to be the only identifiable environmental or behavioral factor linked to the occurrence of myopia, although genetic factors were suspected. Limiting reading is the only practical technique for preventing excessive eye lengthening in children, and corrective lenses, including glasses and contact lenses, represent the primary means for ameliorating eye-length-related disorders, including myopia. The medical community and people with eye-length-related disorders continue to seek better understanding of eye-length-related disorders and methods for preventing, ameliorating, or reversing eye-length-related disorders.